Nobody seems to have replied to this. Did you lose your badass rank at any point? There was a semi-recent patch which fixed lost badass ranks. If your badass rank was recovered, they also awarded you with 10 golden keys.

I play co op and my badass rank was lost, me and my co op partner got keys, he got 10, I'm not quite sure how many I recieved, but his badass rank rose almost 10k points. And he did not ever lose his badass rank.

Despite redeeming a large number of key codes (at least one worth five) and only using a few, BL2 only lists me as having six keys remaining. Based on the codes, I should have at least twice that. Anyone else?

I haven't had anything like that happen. It sounds like the BA reset cause people lost their keys when that happened as well. But if you only lost keys then I haven't heard anyone else saying it happened to them, here or on the gearbox forums.